The purpose of this study is to evaluate the potential use of a defective human immunodeficiency virus (HIV-1) as an expression vector for nondividing cells, and in particular for cells of the central nervous system (CNS). The project addresses several virological elements which must be functional for a gene expression vector, to allow the targeted and stable expression of genes in differentiated, nondividing cells. Such a vector would obviously be very beneficial for many areas of the life sciences. It would also have a potential therapeutic use for several genetic diseases. HIV-1, a retrovirus and a member of the lentivirus family, presents itself as a potential candidate for such a vector: As a characteristic of this virus family, its members are able to translocate their preintegration complexes through the nuclear membrane, which is essential for proviral integration.The project has recently been initiated, and we have completed the assembly of several DNA constructs which will be used to generate and select HIV-1 packaging cell lines for the expression of the structural and regulatory proteins of HIV-1. DNAs which encode several different viral envelope proteins, including murine leukemia virus ecotropic and amphotropic glycoproteins as well as the vesicular stomatitis virus glycoprotein have been cotransfected with HIV- 1 and packaging constructs. Studies are in progress to quantitate defective HIV-1 pseudotype viruses within the cell supernatants by stable transformation. Subsequent studies will focus on the efficiency of proviral integration into nondividing cells, packaging of foreign RNA, viral targeting and stable gene expression. We anticipate that the basic knowledge about these functions on the molecular level, will enable us to develop novel defective virus particles with the described properties for the gene delivery and expression in the CNS.